This invention relates to the recovery of energy from geothermal brines and other hot water sources, and is particularly concerned with a process and system of the aforementioned type, employing direct contact heat exchange between the hot brine or hot water feed, and a working fluid wherein the heated working fluid is expanded to produce work, and the expanded and discharge working fluid is recycled to the heat transfer column, and further providing for reduction of working fluid losses and the use of mixtures, particularly hydrocarbon mixtures, as working fluid.
U.S. Pat. No. 3,988,895 to Sheinbaum discloses power generation from hot brines by passing a hot fluid in direct contact heat exchange relation with working fluid. The working fluid is vaporized and the vaporized working fluid is passed through a power extracting gas expansion device.
Sheinbaum states that in many cases, fluid from a geothermal well may contain a mixture of steam and water and in this case the fluid is advantageously passed through a flash chamber wherein the steam will be separated from the water and the steam passed through a surface contact heat exchanger for transferring the heat from the steam to the working fluid.
The patentee states that any fixed gases that may be present in the steam may be removed at the output of such heat exchanger by passing the condensate through a separator.
Thus, Sheinbaum is primarily concerned with recovering the heat in the steam contained in the geothermal fluid, and only incidentally vents fixed gases.
Further, the above patent discloses use of isobutane only as working fluid. However, under certain conditions of operation use of only a single hydrocarbon such as isobutane as working fluid does not provide maximum energy recovery from the geothermal brine or other hot water feed.
U.S. Pat. Nos. 3,234,734, and 3,516,248 disclose power generation by heating a working fluid which can be in the form of mixtures of organic fluids, in a boiler and utilizing the energy of the heated vaporized fluid to perform work as by expansion in an expansion engine or turbine. However, the working fluid properties and requirements for the process of these patents are substantially different than for a direct contact heat exchange process of the type disclosed in the above Sheinbaum patent.
It is accordingly a chief object of the invention to provide a process and system for recovery of energy from geothermal brines and hot water sources by operation of a heat transfer column providing direct heat transfer between the hot brine or hot water, and a working fluid, expansion of the heated working fluid and recycling of expanded working fluid to the heat transfer column, while minimizing working fluid losses in the system. A further object is to minimize the amount of uncondensible gas vented from the system, and thereby minimize the loss of working fluid vented with such uncondensible gas. Yet another object is the employment of a working fluid in the form of mixtures of certain organic fluids which under certain conditions of operation increases the efficiency of the above direct contact heat transfer process and system, and results in maximum energy recovery.